The present invention relates to methods of transporting proppant particulates in a subterranean formation.
Subterranean wells (e.g., hydrocarbon fluid producing wells and water producing wells) are often stimulated by hydraulic fracturing treatments. In a typical hydraulic fracturing treatment, a treatment fluid is pumped into a wellbore in a subterranean formation at a rate and pressure above the fracture gradient of the particular subterranean formation so as to create or enhance at least one fracture therein. Particulate solids (e.g., graded sand, bauxite, ceramic, nut hulls, and the like), or “proppant particulates,” are typically suspended in the treatment fluid or a second treatment fluid and deposited into the fractures while maintaining pressure above the fracture gradient. The proppant particulates are generally deposited in the fracture in a concentration sufficient to form a tight pack of proppant particulates, or “proppant pack,” which serves to prevent the fracture from fully closing once the hydraulic pressure is removed. By keeping the fracture from fully closing, the interstitial spaces between individual proppant particulates in the proppant pack form conductive pathways through which produced fluids may flow.
In traditional hydraulic fracturing treatments, the specific gravity of the proppant particulates may be high in relation to the treatment fluids in which they are suspended for transport and deposit in a target interval (e.g., a fracture). Therefore, the proppant particulates may settle out of the treatment fluid and fail to reach the target interval. For example, where the proppant particulates are to be deposited into a fracture, the proppant particulates may settle out of the treatment fluid and accumulate only or substantially at the bottommost portion of the fracture, which may result in complete or partial occlusion of the portion of the fracture where no proppant particulates have collected (e.g., at the top of the fracture). As such, fracture conductivity and production over the life of a subterranean well may be substantially impaired if proppant particulates settle out of the treatment fluid before reaching their target interval within a subterranean formation.
One way to compensate for proppant particulate settling is to introduce the proppant particulates into the fracture in a viscous gelled fluid. Gelled fluids typically require high concentrations of gelling agents and/or crosslinker, particularly when transporting high concentrations of proppant particulates in order to maintain them in suspension. As many gelling and crosslinking agents are used in a variety of fluids within and outside of the oil and gas industry, their demand is increasing while their supply is decreasing. Therefore, the cost of gelling and crosslinking agents is increasing, and consequently, the cost of hydraulic fracturing treatments requiring them is also increasing. Additionally, the use of gelling and crosslinking agents may result in premature viscosity increases that may cause pumpability issues or problems with subterranean operations equipment.
Another method of compensating for the settling nature of proppant particulates is the introduction of gas-generating mechanisms that introduce sufficient gas to increase proppant particulate buoyancy within the treatment fluid. However, the gas is often generated at unwanted intervals within the subterranean formation, thereby failing to adequately keep the proppant particulates suspended in the treatment fluid until they reach the target interval. Additionally, gas may be generated partially at unwanted intervals and partially at the desired interval, such that the amount of gas generated at the desired interval is insufficient to increase the buoyancy of the proppant particulates to overcome settling forces.
The degree of success of a hydraulic fracturing operation depends, at least in part, upon fracture conductivity after the fracturing operation has ceased and production commenced. Therefore, a method of hindering the settling of proppant particulates in a treatment fluid may be of value to one of ordinary skill in the art.